docs: def _get_stddevs(self, C, stddev_types, num_sites):
          """
          Return total standard deviation.
          """
          assert all(stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
                     for stddev_type in stddev_types)
  
          if self.DEFINED_FOR_INTENSITY_MEASURE_COMPONENT == 'Random horizontal':
              # Using equation 8 of the paper,
              # corrected as indicated in the erratum
              Sr = np.sqrt(C['SlZ']**2 + (C['S3']/np.sqrt(2))**2)
          else:
              Sr = C['SlZ']
  
          stddevs = [np.zeros(num_sites) + Sr for _ in stddev_types]
          return stddevs